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Abstract

Background

There is little data on the safety of combining radiation therapy and human immunodeficiency
virus (HIV) protease inhibitors to treat cancers in HIV-positive patients. We describe
acute toxicities observed in a series of HIV-positive patients receiving modern radiation
treatments, and compare patients receiving HIV protease inhibitors (PI) with patients
not receiving HIV PIs.

Results

At baseline, the patients in the two groups were similar with the exception of HIV
medication regimens, CD4 count and presence of AIDS-defining malignancy. Patients
taking concurrent PIs were more likely to be taking other HIV medications (p = 0.001)
and have CD4 count >500 (p = 0.006). Patients taking PIs were borderline less likely
to have an AIDS-defining malignancy (p = 0.06). After radiation treatment, 100 acute
toxicities were observed and were equally common in both groups (64 [median 3 per
patient, IQR 1-7] with PIs; 36 [median 3 per patient, IQR 2-3] without PIs). The observed
toxicities were also equally severe in the two groups (Grades I, II, III respectively:
30, 30, 4 with PIs; 23, 13, 0 without PIs: p = 0.38). There were two cases that were
stopped early, one in each group; these were not attributable to toxicity.

Conclusions

In this study of recent radiotherapy in HIV-positive patients taking second generation
PIs, no difference in toxicities was observed in patients taking PIs compared to patients
not taking PIs during radiation therapy. This suggests that it is safe to use unmodified
doses of PIs and radiation therapy in HIV cancer patients, and that it is feasible
to use PIs as a radiosensitizer in cancer therapy, as has been suggested by pre-clinical
results.

Background

HIV and malignancies

Historically, HIV infection is associated with a much higher risk of specific cancers
[1-4]. In particular, diagnosis of Kaposi sarcoma, non-Hodgkin lymphoma (NHL), or cervical
cancer are considered acquired immunodeficiency syndrome (AIDS)-defining malignancies
[5]. However, increasing effectiveness of anti-retroviral therapy (ART) has led to decreased
mortality in Europe and North America from opportunistic infections and AIDS-defining
malignancies [5-8], while mortality from non-AIDS-defining and non-HIV-associated cancers has been increasing
[8,9].

Response to cancer therapy is also different in the HIV patient population. Initial
reports found increased radiotoxicity in HIV patients receiving treatment for Kaposi
sarcoma, cervical carcinoma, while there was no difference in adverse effects of radiation
therapy for other malignancies [10,11]. Systemic glutathione deficiency [12], DNA repair deficiency, or cell cycle dysregulation may increase radiosensitivity
[13-15]. However, radiation therapy remains a cornerstone of therapy in a number of cancers
such as anal cancer [16], prostate [17], breast [18-20], and cervical cancer [16,21].

Protease inhibitors in the treatment of HIV

PIs are anti-viral drugs that inhibit proteases, viral enzymes which cleave polyprotein
precursors into mature viral proteins [22]. PIs are one class of anti-virals that is used as the 'base' in combination with
two 'backbone' drugs for treatment of HIV, antiretroviral therapy (ART). There are
currently ten PIs available; in chronological order of FDA approval, saquinavir, ritonavir,
indinavir, nelfinavir, lopinavir, atazanavir, fosamprenavir (pro-drug of amprenavir,
which is no longer available), tipranavir, and darunavir.

Although PIs act by inhibiting HIV aspartyl protease, they also have off-target effects.
The entire class is associated with dysregulation of glucose and lipid metabolism
due to homology between HIV-1 protease and various human proteins [23-26]. In addition, some PIs inhibit the phosphatidyl-inositol 3-kinase (PI3K)-Akt pathway,
which is shared by numerous cell homeostasis pathways [27,28].

Non-target effects of protease inhibitors

A number of PIs have been associated with anti-cancer activity [29]. Through PI3K-Akt and closely related pathways, PIs induce apoptosis of tumor cells
[30-36]. Although PIs have been shown to directly effect tumor cell death, use of PIs has
not reduced cancer risk in HIV patients, suggesting that PIs would not be clinically
effective anti-cancer monotherapies [37]. Although ineffective alone, PIs synergize with other cancer therapies such as radiotherapy
[38].

Initial studies suggested that nelfinavir upregulates vascular endothelial growth
factor (VEGF) and downregulates hypoxia-inducible factor 1 alpha (HIF-1α). Although
VEGF can increase tumor oxygenation, the HIF1-α hypoxia factor can mediate radiation
resistance [39,40]. However, HIF-1α knockdown studies suggest that radiosensitivity induced by PIs is
independent of HIF-1α [28,40-42]. In a number of cancers, resistance to radiotherapy is mediated by the PI3K-Akt pathway,
suggesting an alternative mechanism of PI-induced radiosensitization [43-45]. Preclinical studies with nelfinavir in head-and-neck cancer [46] and non-small cell lung cancer [28] cell lines found downregulation of Akt to be associated with increased sensitivity
to radiation.

Although PI-induced radiosensitization of cancers was shown to be independent of HIF-1α,
PIs have been shown to induce systemic vascular stress [47]. Preclinical in vivo studies suggest that in addition to direct effect on the tumor cells, PIs may inhibit
PI3K-Akt activation in tumor vasculature, suppressing hypoxia pathways and leading
to reduced radiation resistance [48,49]. Other clinical reports also suggest that PIs and radiotherapy interact on tumor
vasculature similar to the effects of radiation and bevacizumab, an anti-angiogenic
antibody [50].

Protease inhibitors and radiotherapy

A retrospective review (14 patients receiving PIs and 28 controls) did not find severe
toxicities attributable to combination of PIs and radiotherapy for cancer in HIV+
patients [11,51-54]. There are ten prospective trials, nine of which are on-going (a phase II trial was
terminated due to poor enrollment): five phase I studies, and four studies that have
a phase II component. One published phase I trial in pancreatic cancer showed the
following toxicites one of which was life-threatening: severe nausea and vomiting
and increase in liver enzymes and bilirubin due to stent occlusion [55]. Given the inconclusive safety data on combining PIs and radiation therapy to treat
cancer in HIV patients, we reviewed a series of HIV patients receiving radiation therapy
for malignancies.

Methods

Patient identification

In accordance with a research protocol approved by the Institutional Review Board,
patients were identified by review of clinical records from January 1, 2009-October
31, 2010 in the Department of Radiation Oncology at The Johns Hopkins Hospital. Patients
were included if they had documented HIV infection and received radiation therapy
at Johns Hopkins.

Retrospective review

Medical records for included patients were reviewed for HIV medications, cancer diagnosis
and stage, radiation therapy (site, dose, fractionation, completion or early stopping),
age at time of radiation therapy, cancer chemotherapy, acute (< 6 weeks after end
of radiation therapy) toxicities categorized by Common Toxicity Criteria for Adverse
Events version 3.0 (CTCAE) grade. All patients receiving radiation therapy were evaluated
at least once per week for treatment toxicity, and side effects were recorded prospectively
in an electronic record system.

Results

We retrospectively reviewed acute toxicities in a series of patients with a history
of HIV infection and receiving radiation therapy; in this series, we compared patients
who received concurrent PIs with patients who did not receive concurrent PIs. Eighteen
patients received concurrent PIs and radiation therapy; one patient received radiation
therapy for two different malignancies, and one patient received radiation for three
recurrences of NHL. There were eleven patients with a history of HIV infection but
not treated with PIs who received radiation therapy; one patient received three regimens
of radiation therapy, twice for brain metastasis and once for testicular metastasis.

Patient characteristics

Characteristics of patients receiving concurrent protease inhibitor are presented
in Table 1 while characteristics of patients not receiving concurrent protease inhibitor are
presented in Table 2. There were 34 total courses of radiation treatment delivered (21 with PIs, 13 without
PIs) for a variety of histologies, including HIV-defining (0 with PIs; 3 [23%] without
PIs), HIV-associated (11 [58%] with PIs; 5 [38%] without PIs), non-HIV-associated
malignancies (8 [42%] with PIs, 5 [38%] without PIs), and non-malignancies (keloid
scar and dural arteriovenous fistula with PIs, none without PIs). The median age was
50 (interquartile range [IQR] 47-56). The difference between the two groups in number
of AIDS-defining malignancies almost reached statistical significance (p = 0.06),
but the remainder of the malignancies (HIV-associated and non-HIV-associated) are
not differently distributed in the two groups (p = 0.9). 29 cases had documented pre-treatment
CD4 counts; 4 were <50 (4 [24%] with PIs), 13 were <200 (9 [53%] with PIs, 4 [33%]
without PIs), and 21 were <500 (10 [59%] with PIs; 11[92%] without PIs). Patients
taking PIs were more likely than patients not taking PIs to have a CD4 count≥500 (7
[41%] with PIs; 1 [8%] without PIs; p-0.006).

Radiation treatment

For the 29 patients receiving radiation therapy, 15 patients were treated with definitive
or adjuvant dose regimens (9 receiving PIs, 6 without PIs), while 14 patients received
palliative radiation doses (9 receiving PIs, 5 without PIs). The exact definition
of definitive/adjuvant versus palliative dose varied based on body site. Definitive/adjuvant
dose was at least 5400 cGy for brain (conventional fractionation equivalent), 7000
cGy for head and neck, 5400 cGy for breast, 4500 cGy for pelvis, and 7800 cGy for
prostate. Palliative doses also varied based on body site and disease histology, but
were lower than definitive/adjuvant dose regimens.

HIV medications and systemic chemotherapy

Systemic chemotherapy regimens for these two groups of patients are presented (Table
1 and 2). Of the 32 treatments for cancer (19 with PIs, 13 without PIs), 13 included systemic
chemotherapy regimens (7 [37%] with PIs; 6 [46%] without PIs). 21 of the 29 patients
were receiving HIV medications (17 [94%] with PIs; 4 [36%] without PIs; p = 0.001).

In the group receiving PIs, the most common PI was ritonavir (20 [95%]), followed
by darunavir and lopinavir (7 [33%] each), atazanavir (5 [24%]), and only one [5%]
patient received nelfinavir (Table 1 and 2).

Toxicities

Follow-up and observed toxicities are presented in Table 3 and 4. The median follow-up of all patients was 18 weeks [IQR 8-30], but the follow-up
for patients not taking PIs (median 13 weeks [IQR 5-18]) was much shorter than the
follow-up for patients taking PIs (median 21 weeks [IQR 10-38]). The limited follow-up
in the group not taking PIs prevented comparison of long-term toxicities.

There were 64 acute toxicities in the group receiving PIs (30 grade 1, 30 grade 2,
4 grade 3). In the group not receiving PIs, there were 36 acute toxicities (23 grade
1, 13 grade 2). The median number of toxicities experienced per patient was not different
between the groups (3 [IQR 1-7] with PIs; 3 [IQR 2-3] without PIs). Chi-square analysis
of the distribution of severity did not find statistically significant difference
in the severity of toxicities between the two groups (p = 0.38). One radiation treatment
in each group was stopped early, but neither of these was secondary to toxicity (no
grade 3 toxicities in either patient).

Discussion

Our retrospective review of HIV-positive patients receiving radiation therapy found
no increased toxicity in patients receiving concurrent PIs. The number and severity
of toxicities experienced per patient were not found to be different in patients who
were concurrently taking PIs compared to those who were not. There were differences
in the baseline characteristics and medication regimens of the two groups. First,
there were no cases of AIDS-defining malignancies in the group treated with PIs. This
difference coincided with a difference in all HIV treatment and CD4 count. Significantly
more patients in the non-PI group did not receive any medication to manage HIV, and
significantly more patients in the non-PI group had CD4 counts below 500. This difference
may reflect the efficacy of PIs and ART in controlling HIV, and a resulting decrease
in opportunistic malignancies that has been observed with progressive generations
of ART[9]. Although ART is typically initiated if the CD4 count is below 500, there are a number
of other factors that contribute to the decision to initiate therapy, such as patient
preference, adherence to prescriptions, and HIV strain. There was no association between
CD4 count and adverse events.

There have been a number of case reports and small case series documenting seve re
toxicities in HIV patients receiving radiation therapy. A meta-analysis of case reports
and case series found severe toxicities in HIV patients receiving radiation therapy
for Kaposi sarcoma and cervical carcinoma, but not in other malignancies[10]. Our results are in accordance with the only published study evaluating toxicities
from interaction between PIs and radiation therapy [11]. Plastaras et al. reviewed 14 patients with concurrent PIs and 28 patients in the
absence of PI, and found no difference in toxicity from radiation therapy. Although
this group found no increase in toxicity from radiation therapy, the patient series
was treated between 1993-2007 for the control group and 1997-2006 for the PI group.
Inclusion of patients from this time period may have been reflected in the distribution
of PIs and the distribution of malignancies treated. Nearly all patients in the Plastaras
et al. study were treated with nelfinavir, three were treated with saquinavir (the
oldest available PI), and one was treated with amprenavir (no longer available). 29
(69%) of 42 malignancies were AIDS-defining or strongly associated with HIV. These
results may be limited by the baseline characteristics: AIDS-defining and HIV-associated
malignancies are more heavily represented than in the current HIV+ population and
PI regimens are evolving rapidly. Although not related to the years from which the
patients were sampled, only 6 of the 14 patients from the PI group had documented
CD4 count: one was <50, two were <200, and three <500. No association was observed
between CD4 count and radiation toxicity, but the data is limited.

Our study characterizes the safety of radiation therapy combined with the newer generation
of PIs in treatment of non-AIDS defining malignancies which are increasingly common
in the era of improved ART. The series included only patients treated from January
1, 2009 onwards: of the 18 patients receiving PIs, 16 (89%) were receiving a dual-PI
regimen; only two were taking a mono-PI regimen (one ritonavir and one nelfinavir).
The case series included more malignancies not associated with HIV or AIDS (ductal
carcinoma of the breast, renal cell carcinoma, cholangiocarcinoma, and meningioma),
and two non-malignancies (dural AVM, and keloid scar) that were treated with radiation.
Half of the patients in this case series received definitive or adjuvant radiation
dose regimens (45-78 Gy). These patients were distributed equally in the group with
PIs and in the group without PIs, and combination of definitive/adjuvant doses of
radiation with PIs did not increase toxicities over definitive/adjuvant radiation
doses alone. The present study more than doubles the reported number of patients treated
with HIV PIs and radiation from 14 to 32.

The limitations of this study include the small size, short follow-up, heterogeneous
nature of our cohort, and the differences between the control group and the PI treatment
group. As discussed before, in addition to not taking PI, the control group also received
less non-PI HIV medications and had a lower median CD4 count. The factors that underlie
these two differences may confound the results. In addition, although we collected
data on late toxicities, there was insufficient follow-up (21 weeks [IQR 10-38] with
PIs, 13 [IQR 5-18] without PIs) to assess differences in late toxicities. Extended
follow-up is necessary to determine the impact on long term toxicities. In addition,
the majority of the cases received ritonavir combined with a second PI. Ritonavir
does not inhibit Akt, which is a proposed mechanism of radiosensitization by PIs [27]. However, there are no published studies evaluating the radiosensitizing effect of
darunavir, atazanavir, or lopinavir, which were used in combination with ritonavir
by the majority of the patients. Prior studies on radiosensitization by PIs have not
found a defining structural characteristic which would predict whether a PI will increase
radiosensitivity. In spite of these limitations, this retrospective review provides
valuable information about the acute toxicity of combining radiation with current
PI therapies. Review of this contemporary series of patients did not find an increase
in acute toxicity from the combination of the newest generation of HIV PIs and radiation
therapy to treat diverse pathologies.

Conclusions

Preclinical data has suggested that PIs used in the treatment of HIV may radiosensitize
cancer cells, but case reports have suggested that PIs may exacerbate radiotoxicity
in normal tissue. Review of a set of HIV-positive radiation therapy patients did not
reveal increased toxicity in patients taking PIs during radiation therapy. Our cohort
doubles the number of patients in the current literature on the acute safety profile
of combining PIs and radiation therapy. These data suggest that clinical trials of
PIs as radiosensitizers will not encounter increased acute toxicity.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

APS identified the HIV-positive patients receiving radiation treatment, performed
the statistical analysis and helped draft the manuscript. JZ designed the protocol,
collected clinical variables in review of the patient records and helped draft the
manuscript. PTT and ML conceived of the study, designed the study and edited the manuscript.
All authors read and approved the final manuscript.